Electronic Structure and the Periodic Table
(*Make sure to complete Unit 15 of Flinn Prep)
1. Know how to calculate the wavelength, energy and frequency and understand the relationships between these variables.
All electromagnetic light moves at the speed of light (the speed of light in a vacuum, and in air, is constant: c = 2.998 x 10 m/s8 ) Therefore, wavelength and frequency have an inverse
relationship, and all three variables can be related by the following equation:
c =
v
E = hv =
hc
/
wavelength
h = 6.63 x 10 -34 J/sec
c = 2.998 x 10 8 m/s
2. Know the wavelength of visible light is between 4 x 10 -7 – 7 x 10 -7 meters.
Photoelectric Effect
In 1905, Einstein explained the photoelectric effect (when light shines on a clean metal surface and electrons are emitted, but only if enough energy is provided) using Planck’s quantum idea. Only light at or above a threshold freq. will cause e– to be ejected from a metal surface. For
3. Understand that atomic spectra have specific fingerprints and lines that identify the element
Line Spectra
*Ordinary white light is dispersed by a prism into all visible light.
Niels Bohr took Planck’s quantum idea and applied it to the e– in atoms.
Bohr’s assumed his circular orbits had particular energies, given by:
RH =Rydberg constant = 2.180 x 10–18 J
n = 1, 2, 3, ... (the principal quantum number)
When n is very large, En goes to zero, which is larger than anything. Bohr stated that e– could
4. Understand that electrons can gain or lose energy to move energy levels. 5. Be able to write electron configurations
7. Be able to draw orbital diagrams for elements in the ground state; identify ones that are in the excited state, and configurations for ions.
8. Be able to identify the major families on the periodic table: alkali metals, alkaline earth metals, transition metals, halogens, noble gases. Understand the differences between group/family and period/row.
9. Understand Hund’s Law, Aufbau’s Law, and Pauli’s Exclusion principle, and how they can be identified in an orbital diagram.
10. Understand the Periodic trends and why they occur. a. Atomic Radius
b. Ionic Radius c. Ionization Energy d. Electronegativity
Practice Problems
1. You sit in your back yard on a warm summer evening watching the red sky (lambda = 625 nm) at sunset and listening to music from your CD player. The laser has a frequency 3.84 x 10 14 s-1
a. What is the frequency of the radiation from the red sky?
b. What is the wavelength of the laser in nm?
2. Sodium lamps are commonly used to illuminate highways because of their intense yellow orange emissions at 589 nm.
b. Calculate the energy, in kilojoules, of one mole of such photons.
c. To sense visible light, the optic nerve needs at least 2.0 x 10 -17 J of
energy to trigger impulses that reach the brain. How many photons of the sodium lamp emissions are needed to “See” the yellow light?
3. Calculate the wavelength in nanometers of the line in the Balmer series that results from the transition n = 4 to n = 2.
4. Draw the electrons configurations for sulfur, krypton and iron atoms.
5. Draw the electron configuration for the Fe 2+ and Br – ions.
6. Using the periodic table, arrange each of the following in order of increasing size.
a. Mg, Al, Ca b. S, Cl, S
2-c. Fe, Fe 2+, Fe 3+
7. Consider C,N, and Si.
b. Which has the largest ionization energy? The smallest?
REVIEW
Consider Vanadium. There is a line in the Vanadium spectrum at 318.5 nm. a. In what region of the spectrum is this line found?
b. What is the frequency of the line?
c. What is the energy difference between the two levels responsible for this line in kJ per mole?
d. The ionization energy of Vanadium from the ground state is 650.2 kJ/ mol. Assume that the transition in (c) is from the ground state to the excited state. If that is the case, calculate the ionization energy from the excited state.
e. Write the electron configuration for V and V3+ ion.
f. Draw the orbital diagrams for the above.
g. How many unpaired electrons are in each?
ASNWERS: a) ultraviolet
b) 9.413 x 10 14 s -1
c) 376 kJ/mol d) 274 kJ/mol
e) 1s22s22p63s23p64s23d10; 1s22s22p63s23p63d2 f)(see me)
g) 3;2
